1. Field of the Invention
The present invention relates to image formation apparatuses. More particularly, the present invention relates to an image formation apparatus such as a digital copying machine, a printer, and the like to form an image on a photoconductor by exposing the photoconductor according to image density data of each pixel in an original.
2. Description of the Related Art
In an image formation apparatus such as a digital copying machine, an intensity modulation method is known as a conventional method of forming an image on a photoconductor. The intensity of a light beam directed onto a photoconductor is modulated according to image density data of each pixel in the original. This method is advantageous in that high resolution and fine smooth gradation characteristics can be achieved since an image is obtained with the density associated with the read out image density data in a one-to-one correspondence.
In a conventional intensity modulation method, critical control of the density is required in the highlight area. It was not easy to stabilize the tone reproduction. Furthermore, there is a possibility of the graininess of the halftone area being degraded due to generation of random noise. The inventors of the present invention aimed to improve stabilization of tone reproduction and graininess by reducing the duty ratio of the light emission time less than 100% in the intensity modulation method (U.S. Pat. No. 5,189,441). However, a phenomenon was seen of degradation in the resolution due to the fine lines on the image in this method.